There are a number of previously known lighting devices which are designed to simulate flames or candles. An example of a simple gas discharge lamp with parallel plates involves no electronics. In this system the neon gas glows with an orange color and the light bulb flickers. This suffers from a low light output as well as a rapid unrealistic flicker effect, as it is difficult to control the flicker rate.
U.S. Pat. No. 4,839,780, issued to Chuan et al., teaches a simulative candle involving an electric neon bulb powered by an astable DC-to-DC power supply which causes the bulb to flicker.
Another example of electrically-simulated candle flames uses incandescent lamps. The lamps can have one or more filaments that are caused to glow with some manner of modulation or flickering.
U.S. Pat. No. 5,097,180, issued to Ignon et al., teaches a flickering candle lamp which uses multiple independent analog oscillators with the weighted outputs summed together to cause the filament of a single electric bulb to flicker.
U.S. Pat. No. 4,510,556, issued to Johnson, teaches an electronic candle apparatus using a digital shift register to create pseudo-random pulse trains to drive a set of 3 vertically spaced lamps producing varying average brightness: The bulb at the bottom is the brightest and the bulb at the top has the least average brightness.
U.S. Pat. No. 4,492,896, issued to Jullien, teaches a coin operated electronic candle system comprising an array of simulated candles, each of which uses a light bulb with a single filament that is caused to flicker.
These last inventions use incandescent light bulbs which require high power and give off heat. The life of the bulb is shortened by the heating and cooling of the filament caused by the on and off flickering. The single filament devices also suffer from a lack of motion in the simulated flame.
Other known electronically simulated candles use light emitting diodes (LEDs) in place of lamps. For example, U.S. Pat. No. 5,013,972, issued to Malkieli et al., teaches a dual-powered flickering light which use a flip flop or multivibrator to alternately pulse a pair of light emitting diodes on and off to simulate a candle flame.
U.S. Pat. No. 5,255,170, issued to Plamp et al., teaches an illuminated memorial comprising a lucite cross for continuous illumination at night using a single red LED, which is powered by rechargeable batteries. The batteries are rechargeable with a solar cell.
Other devices use LEDs that are flashing to simulate electronic candles. The LEDs are typically of a single color, and use repetitive and very limited simulated pattern.
The discussed prior-art electronic flame or candle simulations cover a range of known approaches to electronic simulation of flames or candles. The utilized circuits, some having a simulated flicker, typically result in a flame simulation that appears static or repetitive after a very short time of observation due to the limited pattern length and the lack of variety. The prior-art flame or candle simulations may not be relaxing or soothing to a viewer because of their fatiguing viewing patterns.
Even with multiple lighting elements, prior art flame or candle simulations fail to realistically simulate the randomness of a flame, especially when viewed over a length of time. Some of these previously known devices rely on a "flicker" effect by pseudo-randomly turning on and off the lighting elements. This known simulation approach typically yields flickers with a noticeable repetitive pattern. The devices also typically suffer from a limited number of discrete intensity levels, with some having as few as two, on and off. Yet, other devices which use an analog circuitry often suffer from an absence of flicker randomness.
What is then needed is an electronic flame or candle simulation with time-changing simulated flame patterns, possibly including color patterns, to better engender soothing and visually pleasing lighting effects.